Elemental Stoichiometry Research Articles

Structural, dielectric and ac electrical properties of nano-structured Mn0.6Co0.2Ni0.2Fe2O4 ternary ferrite synthesized by citrate-gel auto-combustion technique

The present paper reports the structural, dielectric and ac electrical properties of nanoparticles of mixed polycrystalline spinel ferrite ternary compound Mn0.6Co0.2Ni0.2Fe2O4 synthesized by using the citrate-gel auto-combustion technique. The standard characterization techniques such as EDAX, XRD and FTIR were primarily employed to confirm the elemental stoichiometry, crystallized single-phase, IR-functional groups. These measurements ascertained the formation of monophasic and pure ferrite compound. The powder X-ray diffraction analysis was done to determine the lattice constant(0.8420 nm), crystallite size(21 nm), X-ray density (5.16 g/cm3), distribution of cations among the tetrahedral and octahedral sites of spinel lattice(with iron-Fe3+ distribution ratio among A and B sites is 0.25), bond angles and bond lengths. The theoretical lattice constant is found to be 0.8422 nm. The nature and position of the IR-bands were observed through FTIR spectroscopy. The high-frequency band v1 (A-site vibrations) lies at 563.07 cm-1 while the low-frequency band v2 (B-site vibrations) lies at 462.59 cm-1 . The force constants for the tetrahedral site (kt) and octahedral site (ko) were deduced 1.33×102 N/m and 1.27× 102 N/m, respectively. Frequency dependence of dielectric constant and tangent loss has been explained by the Maxwell Wagner model and Koop's theory. The Jonscher’s power low was used to describe the ac conductivity measurements. The Nyquist and cole-cole plots indicated presence of grain contribution in the conduction mechanism.

Stoichiometric imbalances and the dynamics of phosphatase activity and the abundance of phoC and phoD genes with the development of Cunninghamia lanceolata (Lamb.) Hook plantations

Soil phosphatase and P-cycling functional genes, such as phoC and phoD, are crucial factors in regulating terrestrial P cycling, especially in highly weathered subtropical and tropical soils. Soil element stoichiometry (especially available C:N:P by measuring dissolved organic C (DOC):available N (AN):Olsen P plays an essential role in biogeochemical P cycling, but how it affects phosphatase activity and the abundance of phoC and phoD genes following afforestation is unclear. Here, we investigated how soil C:N:P stoichiometry affected the dynamics of soil phosphatase activity and the abundance of phoC and phoD genes in an age sequence of 6-, 12-, 18-, 25-, 32-, and 49-year-old Chinese fir plantations. The results showed that the phosphatase activity and the abundance of phoC gene were overall higher in 18- and 25-year-old plantations than in the other four plantations. The abundance of phoD gene gradually increased with stand age. Phosphatase activity significantly and positively correlated with DOC:Olsen P and AN:Olsen P ratios, but not with DOC:AN ratio. Soil phosphatase activity significantly positively correlated with phoC gene abundance, but not with phoD gene abundance, indicating that the phoC gene abundance is the dominant predictor of the microbial functional potential for secreting phosphatase. Further analysis suggested that the ratios of DOC:Olsen P and AN:Olsen P, total N, DOC, AN, Olsen P, and microbial biomass C were the main predictors of phoC gene abundance and that DOC:AN, total P, AN, Olsen P, and microbial biomass C were the main predictors of phoD gene abundance. These findings together highlight the importance of soil available element stoichiometry regulating microbial functional genes, with potential implications for subtropical and tropical biogeochemical processes and for understanding how soil available C:N:P stoichiometry regulates P biotransformation.

Modeling the elemental stoichiometry and silicon accumulation in diatoms

Diatoms are important microorganisms involved in global primary production, nutrient cycling, and carbon sequestration. A unique feature of diatoms is their silica frustules, which impact sinking speed, defense against predators and viruses, and growth cycling. Thus, frustules are inherently linked to their role in ecosystems and biogeochemical cycles. However, constraints on cellular silicon levels remain unclear and few existing models resolve diatom elemental stoichiometry to specifically include variable silicon levels. Here, we use a coarse-grained model of the diatom,Thalassiosira pseudonana, compared with laboratory results to illustrate the relationship of silicon uptake with elemental stoichiometry of other nutrients. The model-data comparison suggests the balance between growth rate and silicon uptake constrains the amount of cellular silicon. Additionally, it expresses relationships between silicon, nitrogen, phosphorus, and carbon to changing growth rates in nitrogen-limited and phosphorus-limited regimes. First, our model-data comparison suggests Si uptake hits a maximum cellular quota at low growth rates and below this maximum there is independent Si uptake. In each nutrient regime, Si:N, Si:P, and Si:C decrease exponentially with growth rate when Si is below the maximum limit. This is explained by independent Si uptake and increased loss of Si to new cells. These results provide predictions of diatom stoichiometry and allocation, which can be used in ecosystem models to differentiate phytoplankton types to better represent diatoms' contribution to global biogeochemical cycles and ecosystems.

Spatial-Temporal Variation of N, P, and K Stoichiometry in Cropland of Hainan Island

Elemental stoichiometry reflects the interaction between plants, soil, and microorganisms, and links biogeochemical patterns with physiological limitations. The stoichiometry of elements in farmland soil is an important part of the function of the agroecosystem. Soil nitrogen (N), phosphorus (P), and potassium (K) are the main macronutrients in terrestrial ecosystems, which are closely related to biogeochemical cycles. Studying the temporal and spatial variability of soil nutrients in tropical farmland is of great significance for exploring the variation of soil nutrients and promoting the sustainable development of tropical agriculture. In this study, soil samples in the farmland of Hainan Island were collected at three different stages for exploring temporal and spatial variations of N, P, and K stoichiometry. Results showed that soil concentrations of available N, P, and K changed markedly with the temporal and spatial variability. The highest available N, P, and K concentrations appeared at the stage of 2016–2020 with values of 110.40 mg/kg, 51.91 mg/kg, and 82.76 mg/kg, respectively, while their lowest values were observed in 2010–2015 with 66.34 mg/kg, 11.27 mg/kg, and 45.77 mg/kg, respectively. The available nitrogen content in the three time periods first increased and then decreased with the increase of available potassium content, an opposite trend was observed between available nitrogen and phosphorus. The content of N increased in Haikou, Lingao, Ding’an, and P increased in Wengchang, and Lingshui and K increased in Danzhou and Wanning as time increased.

Phytoplankton antioxidant systems and their contributions to cellular elemental stoichiometry

AbstractOxidative stress plays a role in many aspects of cellular metabolism, and as a result, antioxidants have the potential to impact cellular stoichiometry and biogeochemical cycles. We reviewed how antioxidant systems influence macronutrient and micronutrient stoichiometry in marine phytoplankton and identified that antioxidant systems have important implications for micronutrient stoichiometry. By leveraging diatom proteomic data, we empirically estimated the level of micronutrient quota variation that can be attributed to antioxidant systems. Fe‐containing antioxidant expression may contribute to 3.3–10 μmol : mol variation in Fe : C, and superoxide dismutases appear to be important contributors to variation in Mn, Ni, Zn, and Cu quotas in phytoplankton. Critical next steps for the study of phytoplankton antioxidant systems are to (1) distinguish between oxidative stress and redox‐based gene regulation and (2) determine how antioxidants influence variation or consistency in micronutrient quotas under various environmental conditions.

Methods for neutron diffraction studies on hydride superconductors and other metal hydrides

High-pressure neutron diffraction is an extremely useful technique in the quest for making and understanding novel hydride superconductors. Neutron diffraction can be used to directly determine elemental stoichiometries and atomic positions of many light elements such as hydrogen or deuterium, even in the presence of heavy elements such as rare-earth metals. Here, we report on the current status and ongoing developments on high-pressure neutron diffraction for hydride superconductors and other metal hydrides with a special focus on current advancements at the Spallation Neutrons and Pressure (SNAP) beamline of the Spallation Neutron Source at Oak Ridge National Laboratory. For broader context, an overview of high-pressure neutron diffractometers and pressure cells is included together with insight into critical sample considerations. There, attention is given to the requirements for powdered hydride samples and the need for deuterium rather than hydrogen. Additionally, the advantages of angular access and data representation as possible at SNAP are described. We demonstrate the current capability for high-pressure neutron diffraction on two different samples created via hydrogen gas loading, specifically pure deuterium and nickel-deuteride. The deuterium example highlights the usefulness of adding sample materials that facilitate the formation of a good powder while the nickel-deuteride example demonstrates that atomic deuterium positions and stoichiometry can be directly determined. Both examples highlight the importance of large scattering apertures. These enable investigation of the data resolved by scattering angle that is needed to identify parasitic peaks and background features. Finally, future directions beyond current high-pressure neutron powder diffraction are also discussed.

The importance of allochthonous organic matter quality when investigating pulse disturbance events in freshwater lakes: a mesocosm experiment

Extreme precipitation is occurring with greater frequency and intensity as a result of climate change. Such events boost the transport of allochthonous organic matter (allo-OM) to freshwater ecosystems, yet little is known about the impacts on dissolved organic matter (DOM) quality and seston elemental stoichiometry, especially for lakes in warm climates. A mesocosm experiment located in a Turkish freshwater lake was designed to simulate a pulse event leading to increased inputs of allo-OM by examining the individual effects of increasing water colour (HuminFeed®, HF), the direct effects of the extra energetic inputs (alder tree leaf leachate, L), and the interactions of the single treatment effects (combination of both sources, HFL), along with a comparison with unmanipulated controls. Changes in the DOM quality and nutrient stoichiometry of the allo-OM treatment additions was examined over the course of the experiments. Results indicated that there was an increase of high recalcitrant DOM components in the HF treatment, in contrast to an increase in less aromatic microbially derived molecules for the L treatment. Unexpectedly, seston C:P ratios remained below a severe P-limiting threshold for plankton growth and showed the same temporal pattern in all mesocosms. In contrast, seston N:P ratios differed significantly between treatments, with the L treatment reducing P-limiting conditions, whilst the HF treatment increased them. The effects of the combined HFL treatment indicated an additive type of interaction and chlorophyll-a was highest in the HFL treatment. Our results demonstrate that accounting for the optical and stoichiometric properties of experimental allo-OM treatments is crucial to improve the capacity to explain extrapolated conclusions regarding the effects of climate driven flooding on freshwater ecosystems in response to global climate change.Graphical abstract

Decoupling of P from C, N, and K Elements in Cucumber Leaves Caused by Nutrient Imbalance under a Greenhouse Continuous Cropping System

There is insufficient information regarding the stoichiometric variation and coupling status of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) in the leaves of nutrient-enriched greenhouse agroecosystems with increasing planting time. Therefore, we assessed the variation in elemental stoichiometry ratios in soil and cucumber (Cucumis sativus L.) leaves, and the coupling status of elemental utilization in the leaves under continuous cropping systems using natural (only soil; i.e., control soil, CO) and artificial (soil + straw + chicken + urea; i.e., straw mixture soil, ST) soil via monitoring studies for 11 years in a solar greenhouse. Soil organic C, total N, and total P concentrations increased by 63.4%, 72.7%, and 144.3% in the CO, respectively, after 11 years of cultivation (compared to the first year), and by 18.1%, 24.3%, and 117.7% in the ST under continuous cropping conditions, respectively. Total K concentrations remained unchanged in both soils. Moreover, the availability of these soil elements increased to different degrees in both soils after 11 years of planting. Additionally, the leaf P concentration increased by 9.8% in the CO, while leaf N and K concentrations did not change, suggesting decoupling of P utilization from that of N and K in leaves under a continuous cropping system. These findings suggest that imbalanced soil nutrients under continuous cropping conditions results in decoupling of P from N and K in the utilization of leaf nutrients.

AACVD processed binary amorphous NiVOx coatings on Cu substrates: Surface characterization and corrosion resistant performance in saline medium

Cu corrosion is a major issue affecting the structural integrity and efficient performance of Cu components in several applications. In recent years, the utilization of metal oxide thin films on copper components is fascinated cumulative consideration particularly in the field of energy and electronic related materials like micro-electromechanical, energy storage and memory device components. Herein, we report the use of a rapid and reproducible approach of aerosol-assisted (AA) CVD for depositing bimetallic nickel-vanadium oxide (NiVOx) thin films directly on Cu substrates. NiVOx coatings were produced by increasing the deposition period from 1 to 3 h at a fixed temperature of 480 °C and were structurally characterized through XRD analysis, XPS, SEM/EDS, and AFM. Detailed characterization was performed for the as-prepared amorphous NiVOx binary films having a compact and dense microstructure at an elemental stoichiometry of Ni/V in 1:1 ratio. Corrosion analyses, including electrochemical frequency modulation, Tafel plot analysis, and dynamic electrochemical impedance spectroscopy, were performed to assess the corrosion resistance performance of binary films on Cu substrates in saline medium. Moreover, scanning electrochemical microscopy was accomplished to estimate the electrochemical stability of the as-processed binary films during the 24-h immersion period in NaCl.

Characterizations of Spray Deposited CdTe Thin Film

The spray pyrolysis is promising technique for deposition of CdTe thin film. We deposited CdTe thin film on glass substrate by homemade spray pyrolysis technique at substrate temperature 3000C. The CdTe thin film was characterized through Field scanning electron microscopy (FSEM), Energy dispersive X-ray analysis (EDAX), Uv-Visible spectroscopy. The SEM micrograph shows the film was uniform coverage, large number of densely packed grain whosesizes ranging from 474nm to 1.64µm. From EDAX analysis conform that the presenceof Cd and Te in prepared film with elemental stoichiometry of Cd and Se was 50.28% and 49.72% respectively. The optical absorption coefficient of the film of order of 106 and band gap of the film 1.45eV.

Structural and weak antilocalization analysis of topological single-crystal SnSb2Te4

Here, we report successful single crystal growth of SnSb2Te4 using the self-flux method. Unidirectional crystal growth is confirmed through X-ray Diffraction (XRD) pattern taken on mechanically cleaved crystal flake while the rietveld refined Powder XRD (PXRD) pattern confirms the phase purity of the grown crystal. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) image and Energy Dispersive X-Ray analysis (EDAX) confirm crystalline morphology and exact stoichiometry of constituent elements. Vibrational Modes observed in Raman spectra also confirm the formation of the SnSb2Te4 phase. DC resistivity (ρ-T) measurements confirm the metallic character of the grown crystal. Magneto-transport measurements up to±5T show a non-saturating low magneto-resistance percentage (MR%). V-type cusp and Hikami Larkin Nagaoka (HLN) fitting at lower field confirms the Weak Anti-localization (WAL) effect in SnSb2Te4. Density Functional Theory (DFT) calculations were showing topological non-trivial electronic band structure. It is the first-ever report on MR study and WAL analysis of SnSb2Te4 single crystal.

Leaf Elemental Concentrations, Stoichiometry, and Resorption in Guam’s Coastal Karst Forests

Greater knowledge concerning the interspecific diversity of the plant leaf ionome is required to effectively understand the spatiotemporal dynamics of biogeochemistry, but Micronesia has been ignored in this literature. The objectives of this study were to quantify the leaf ionome, resorption efficiency, and stoichiometry of leaves from 25 plant species representing Guam’s coastal karst forests. Carbon and nitrogen were quantified by dry combustion, and other minerals and metals were quantified by spectrometry. Nitrogen and calcium concentrations in Guam’s green leaves exceeded the published global means, but manganese and copper concentrations were less than the global means. The remainder of the elements were within the expected ranges. Nutrient resorption rates exhibited a decreasing order of potassium > phosphorus > nitrogen > zinc > copper. The term “accretion efficiency” is introduced to describe the accumulation of an element throughout leaf aging and senescence, and calcium and iron exhibited substantial accretion efficiency in this study. Stoichiometry relations indicated that Guam’s karst forest is most limited by phosphorus and then secondarily limited by nitrogen, although several individual taxa exhibited co-limitation by potassium. Five of the species are officially listed on extinction threat lists. Of these, the Malvaceae tree Heriteria longipetiolata exhibited leaf traits depicting the most recalcitrant litter characteristics, and the Fabaceae tree Serianthes nelsonii exhibited leaf traits depicting the most labile litter characteristics. The contributions of these two tree species to spatiotemporal diversity in biogeochemistry appear to be profound, indicating species recovery efforts are of paramount importance for maintaining ecosystem function and soil heterotroph biodiversity in northern Guam.

Variation in plant carbon, nitrogen and phosphorus contents across the drylands of China

Abstract Determining large‐scale patterns of plant elemental concentrations and stoichiometry along environmental gradients is critical for understanding plant adaptive strategies and predicting ecosystem biogeochemistry processes. However, it remains unclear as to how plant carbon (C), nitrogen (N) and phosphorus (P) concentrations and their stoichiometry in different organs (leaves, stems and roots) respond to large‐scale environmental gradients in drylands. We determined C, N and P concentrations and their ratios in leaves, stems and roots of plants growing in the dryland ecosystems of China. Using threshold indicator taxa analyses, we identified indicator species of plant C, N and P responses to aridity and soil properties. The arithmetic averaged concentrations of C, N and P in drylands were 414, 18.7 and 1.38 mg/g for leaves respectively; 445, 12.1 and 1.08 mg/g for stems respectively; and 418, 10.5 and 0.89 mg/g for roots respectively. The C:N, C:P and N:P ratios were 25.2, 386 and 16.3 for leaves respectively; 42.8, 592 and 14.8 for stems respectively; and 46.8, 658 and 15.6 for roots respectively. Aridity and soil pH generally exerted positive effects on plant N and negative effects on C and P concentrations and, thus, were related negatively to C:N ratios and positively to C:P and N:P ratios. The C, N and P concentrations in organs generally increased with increasing corresponding soil C, N and P concentrations. Shrubs were mainly positive indicators of plant C, N and P concentrations in response to aridity and soil pH, and negative indicators of soil nutrients. In contrast, herbaceous species were mainly positive indicators of soil nutrients and negative indicators of aridity and soil pH. These findings indicate that plants tend to accumulate N rather than C and P with increasing aridity and soil pH. The identification of indicator species for plant elements in response to aridity and soil traits informs our understanding of species‐specific biogeographic patterns of organ elements and potential adaptive strategies of plants in drylands. A free Plain Language Summary can be found within the Supporting Information of this article.

Finding Liebig's law of the minimum.

Liebig’s law of the minimum (LLM) is often used to interpret empirical biological growth data and model multiple substrates co‐limited growth. However, its mechanistic foundation is rarely discussed, even though its validity has been questioned since its introduction in the 1820s. Here we first show that LLM is a crude approximation of the law of mass action, the state of art theory of biochemical reactions, and the LLM model is less accurate than two other approximations of the law of mass action: the synthesizing unit model and the additive model. We corroborate this conclusion using empirical data sets of algae and plants grown under two co‐limiting substrates. Based on our analysis, we show that when growth is modeled directly as a function of substrate uptake, the LLM model improperly restricts the organism to be of fixed elemental stoichiometry, making it incapable of consistently resolving biological adaptation, ecological evolution, and community assembly. When growth is modeled as a function of the cellular nutrient quota, the LLM model may obtain good results at the risk of incorrect model parameters as compared to those inferred from the more accurate synthesizing unit model. However, biogeochemical models that implement these three formulations are needed to evaluate which formulation is acceptably accurate and their impacts on predicted long‐term ecosystem dynamics. In particular, studies are needed that explore the extent to which parameter calibration can rescue model performance when the mechanistic representation of a biogeochemical process is known to be deficient.

Elemental Composition and Cell Mass Quantification of Cultured Thraustochytrids Unveil Their Large Contribution to Marine Carbon Pool

The element stoichiometry of bacteria has received considerable attention because of their significant role in marine ecosystems. However, relatively little is known about the composition of major structural elements of the unicellular heterotrophic protists—thraustochytrids, despite their widely recognized contribution to marine nutrient cycling. Here, we analyze the cell volume and elemental C, N, H, and S cell content of seven cultured thraustochytrids, isolated from different marine habitats, in the exponential and stationary growth phases. We further derive the relationships between the cell volume and elemental C and N content of the cultured thraustochytrids. The cell volumes varied significantly (p < 0.001) among the isolates, with median values of 96.9 and 212.5 μm3 in the exponential and stationary phases, respectively. Our results showed a significantly higher percentage of C (64.0 to 67.5) and H (9.9 to 13.2) but a lower percentage of N (1.86 to 2.16) and S (0.34 to 0.91) in the stationary phase, along with marked variations of C and N fractions among isolates in the exponential phase. The cell C (5.7 to 203.7 pg) and N (0.65 to 6.1 pg) content exhibited a significant (p < 0.001) linear relationship with the cell volume (27.7 to 510 μm3). On further analysis of the relationship across the two growth phases, we found the equation (cell C (pg) = 0.356 × cell volume (μm3) + 20.922) for stationary phase cells more appropriate for C estimation of natural thraustochytrids. This study provides the first experimental evidence of higher cell C density than the current estimate and relatively larger C contribution of thraustochytrids than bacteria to the marine organic pool.

Hydrothermal growth method for the deposition of ZnO films: Structural, chemical and optical studies

Hydrothermal growth method was used to grow the zinc oxide (ZnO) thick films on ZnO seed layer previously deposited by RF magnetron sputtering technique. The effect of introducing of zinc acetate and chloride salts on the structure, chemical and physical properties of the obtained films was investigated. Scanning electron microscope (SEM) and atomic force microcopy (AFM) were utilized to both justify the nanostructure growth of the ZnO thick films deposited by hydrothermal growth method, and to identify their morphology. Energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the elemental stoichiometry of the prepared ZnO thick films with low contamination. X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR) characterizations approved the texturation of the ZnO thick films prepared by hydrothermal growth method and verified the nonstructural growth with (002) preferred orientation as well as hexagonal phase. XRD technique indicated that the ZnO films had a good quality (big grain size and preferential orientation) and the Raman and FTIR studies confirmed the XRD results. Moreover, photoluminescence (PL) spectroscopy verified the optoelectronic behavior and demonstrated a potential optical application in this field.

Does growth rate affect diatom compositional response to temperature?

ABSTRACT Temperature is one of the environmental factors that most strongly influence the life of microalgae, from the enzymatic level up to the modification of biosynthetic and degradation potential and, thus, cellular composition. When exposed to a change in environmental milieu two main responses can be attained by cells: acclimation or homoeostasis. Recent studies testing the impact of other environmental factors indicated that the choice between these strategies is related to growth rates, i.e. cells dividing at a faster rate showed inclination to acclimation while cells dividing at a slower rate were more prone to homoeostasis. These findings motivated us to further explore the extent to which these compositional response modes are applied under varying temperature. Two representative marine diatoms, one centric, Thalassiosira pseudonana, and one pennate, Cylindrotheca fusiformis were investigated. Species were cultured at 15°C, 20°C and 30°C and at two growth rates. Compositional response was analysed with respect to elemental stoichiometry (carbon, nitrogen, silica, phosphorus, sulphur, manganese, iron, zinc and copper) and the major organic pool ratios (carbohydrate:lipid, carbohydrate:protein and protein:lipid). While T. pseudonana exhibited an acclimation response to temperature, C. fusiformis proved to be strongly homoeostatic. In the case of T. pseudonana, our data showed that the variations in composition were consistent with the growth rate dependence hypothesis for many micronutrients, but not for carbon and nitrogen contents, and C:N ratio. These species-specific differences in response mode highlight the diversity in ecophysiological strategies of diatoms, which needs to be considered when predicting climate change responses.

Microstructural analysis and thermoelectric performance of Ga-doped ZnO/reduced graphene oxide thin film nanocomposites

In this work, n-type Ga-doped ZnO (GZO)/reduced graphene oxide (rGO) thin-film nanocomposites were investigated as an approach to enhancing the electron transport of a popular material having weak thermoelectric properties. Namely, the rGO contents of 1, 3, 5, and 7 wt% were mixed in the matrix of chemically derived GZO. The XRD, Raman, XPS spectroscopies, and SEM mapping indicated and confirmed the presence of rGO in the thin-film nanocomposites having good density, nanoscale grains, and stoichiometry of elements in the composition. In this case, rGO sheets enclosed in the grain boundaries of polycrystalline GZO behaved as bridge, which facilitated electron transport and effectively improved the thermoelectric performance of the film nanocomposites. Consequently, the magnitude of the electrical conductivity and power factor of the samples increased by four to five times larger than those of rGO-free GZO ones in the range from room temperature to 400 °C. The obtained results provide promising perspectives of a binary composite material made of environmentally benign, earth-abundant elements, and fabricated by a simple and low-cost process for thermoelectric applications.

Long-term fertilization modifies the mineralization of soil organic matter in response to added substrate

The turnover of SOC in soils is strongly influenced by the availability of substrate and nutrients, especially nitrogen (N) and phosphorus (P). Here, we assessed how long-term fertilization modified SOM mineralization in response to added substrate in a tropical forest. We carried out a 90-day incubation study in which we added two structurally similar compounds which differed in microbial metabolic availability: corn cellulose or corn starch to soils collected from a long-term (11 years) factorial N and P fertilization experiment site in a tropical forest in south China. We measured total soil mineralization rate (CO2 efflux) to characterize SOM mineralization and using 13C isotope signatures to determine the source of the CO2 (original soil C or added substrate) and assessed changes in extracellular enzyme activities: acid phosphomonoesterase (AP), β-1,4-glucosidase (BG), β-1,4- N-acetaminophen glucosidase (NAG), phenol oxidase (PHO) and peroxidase (PER), and microbial biomarkers to determine whether nutrient stoichiometry and decomposer communities explain differences in SOM mineralization rates. Total C mineralization increased substantially with substrate addition, particularly cellulose (5.38, 7.13, 5.58 and 5.37 times for N, P, NP fertilization and CK, respectively) compared to no substrate addition, and original soil C mineralization was further enhanced in long-term N (3.40% and 5.18% for cellulose and starch addition, respectively) or NP (35.11% for cellulose addition) fertilized soils compared to control treatment. Enzyme activities were stimulated by the addition of both substrates but suppressed by P-fertilization. Addition of both substrates increased microbial investment in P-acquisition, but only starch addition promoted C investment in N-acquisition. Finally, fungal abundance increased with substrate addition to a greater extent than bacterial abundance, particularly in cellulose-amended soils, and the effect was amplified by long-term fertilization. Our findings indicate that SOM mineralization might be enhanced in N and P enrichment ecosystems, since the litter input can liberate microbes from C limitation and stimulate SOM mineralization if N and P are sufficient. Our study further demonstrates that structurally similar substrates can have distinct effects on SOM mineralization and the extent of SOM mineralization is strongly dependent on elemental stoichiometry, as well as the resource requirements of microbial decomposers.

Integration of complete elemental mass-balanced stoichiometry and aqueous-phase chemistry for bioprocess modelling of liquid and solid waste treatment systems – Part 1: The physico-chemical framework

Bioprocesses interact with the aqueous environment in which they take place. Currently integrated bioprocess and three-phase (aqueous–gas–solid) multiple strong and weak acid/base system models are being developed for a range of wastewater treatment applications, including anaerobic digestion, biological sulphate reduction, autotrophic denitrification, biological desulphurization and plant-wide wastewater treatment systems. In order to model, measure and control such integrated systems, a thorough understanding of the interaction between the bioprocesses and aqueous-phase multiple strong and weak acid/bases is required. This first in a series of five papers sets out a conceptual framework and methodology for deriving bioprocess stoichiometric equations. It also introduces the relationship between alkalinity changes in bioprocesses and the underlying reaction stoichiometry, which is a key theme of the series. The second paper develops the stoichiometric equations for the main biological transformations that are important in wastewater treatment. The link between the modelling and measurement frameworks, which uses summary measures such as chemical oxygen demand (COD) and alkalinity, is described in the third and fourth papers. The fifth paper describes an equilibrium aquatic speciation algorithm which can be combined with bioprocess stoichiometry to provide integrated models of wastewater treatment processes.